1. Field of the Invention
This invention relates to a collapsible bicycle. In particular, this invention relates to a bicycle having separate rigid main and rear frame members joined together by concentric members forming the seat tube and foldable thereabout.
2. Prior Art
Foldable bicycle technology is replete with a number of constructions attempting to accomplish folding operations yet provide satisfactory bicycle performance. Many of these prior art constructions are technically deficient, requiring difficult, time-consuming operations to collapse or assemble the bicycle or, not providing for adequate riding dynamics when operated. Additionally, given stringent safety requirements, the vast number of prior art proposals are unacceptable in the first as not satisfying contemporary safety rules. For example, many frames which are not permanent structurally integral members are deemed to have inadequate strength characteristics necessary for contemporary bicycle design. Frame systems shown in U.S. Pat. No. 607,325 and U.S. Pat. No. 640,680 are characteristic of a number of prior art frame members which are hinged, telescoping, and the like. While a reduction in size of the bicycle frame is effectuated by those techniques, it requires changes in the strength capacity of the individual frame elements and would not guarantee the fail safe design that is necessary for present day Government approval. In U.S. Pat. No. 607,325, the top tube is sleeved and joined by a collar a. The down tube D is hinged into two portions. Such constructions, while offering foldability, should the hinging or sleeving mechanism come loose the bike does not afford adequate frame rigidity and strength and would be dangerous.
A contemporary example of a foldable bicycle configuration having a rigid front frame is found in U.S. Pat. No. 4,022,485. In this prior art system, the collapsible bicycle includes a rigid main frame while having a collapsible rear frame which is hinged and foldable about a pin located at the pedal housing. However, the rear frame is not a rigid member but rather, a series of segments having pivoting portions to allow the rear frame elements to collapse into a storage position over the rigid main frame. Again, should the pin come loose, the bike would collapse.
Another prior art attempt at achieving a folding bicycle having relatively rigid main and rear frame members is found in U.S. Pat. No. 3,374,009. In this system, the rear frame elements comprising the seat tube 2, the chain stays 5, and the seat stays 7 form a rigid integral assembly. However, the down tube comprises two sections 14 and 15 hinged at a point of articulation 16. Hence, while the necessary structural strength required to support the seat is effectuated by a rigid rear frame member, inherent weakness in the front frame is apparent.
The prior art is however replete with a number of systems having rigid front and rear frames which are foldable to achieve a portable bicycle configuration. Typical of these devices are U.S. Pat. Nos. 3,710,883 and 4,067,589. While portability is achieved, these systems suffer from other defects. First, the number of frame elements is complicated, the locking mechanisms difficult to work, and, most importantly, the bicycles when assembled do not offer satisfactory performance. The hallmark characteristics of all satisfactory foldable bicycle configurations currently in existence is the use of small wheels coupled with high frame weight. The use of such wheels increases the rolling friction, alters the center of gravity of the bicycle, and therefore, does not afford to the user those riding characteristics of a large bike which are required. This inadequacy is made more conspicuous by the frame weight that hinders riding dynamics. As noted in "Better Bikes", Cuthbertson, Ten Speed Press (1980) these folding bikes have poor riding characteristics. The advent of lightweight 10-speed bicycles utilizing full size, typically 27 inch wheels provides a model for an acceptable folding bicycle configuration that should attempt to use those same standard components yet at the same time reduce weight.
The use of standard components, such as full size wheels, brake assemblies, gear chain mechanisms and the like, reduces costs and increases serviceability of the bicycle by relying solely on commercially available components. Secondly, a standing requirement exists in this field for the reduction of weight of the bicycle frame itself. In addition to reducing the overall size of the bicycle, portability implies the ability to easily transport the bicycle in a folded condition. Hence, even if folded, the bicycle should form a "package" that can be conveniently handled. In an extreme example, backpacking, a folded bicycle should be within a weight range to allow transportation on the back of a person. Such a bicycle is not known in the technology. In a more conventional example, portability during travel on airlines or the like, the bicycle should be not only compact in size but easily handled in terms not having projecting parts, and shielding the gear mechanism. Ideally, one wheel of the folded bicycle, such as the rear wheel should provide rolling support so that the "package" can be moved without lifting. Accordingly, there still exists in this technology a need for a foldable bicycle, one using standard components, one satisfying existing safety requirements needed for commercial manufacturing, yet achieving the necessary performance characteristics attained in conventional lightweight 10-speed bicycles.